The present invention relates to a multiprocessor system controlled by a single operating system (OS) and having a plurality of central processor units (CPU's) and, more particularly, to a multiprocessor system permitting expansion of the virtual memory capacity of the system without significantly affecting the OS thereof.
Generally, irrespective of which one of plural CPU's executes the OS, it is necessary for the OS to be able to refer to every area in itself and in the user program.
Because of this need, in this kind of prior art multiprocessor system, every CPU has a virtual memory of the same capacity. Thus, every CPU has a common number of bits indicating an address, and the address section of a command and the area in which to store the address are as large as that number of bits.
Such a technique has been described in a manual entitled "OS/VS2 System Logic Library, Volumes 2 and 4" pp. 2-255 to 2-280 and 4-115 to 4-117.6, published in October 1979 by International Business Machines Corporation, and the gazette of the U.K. Patent No. 1509393.
Meanwhile, the size of an executable program is limited by that of the virtual memory. Therefore, to execute a larger program, the virtual memory capacity has to be expanded.
To expand the virtual memory capacity to satisfy this requirement, the number of bits for an address can be increased sufficiently for the OS to be able to refer to the whole expanded virtual memory. However, addresses in the address sections of commands and the address storage area would have to be revised to reflect the increased number of bits. Therefore, there is the disadvantage that, if this method is used, the hardware structure of each CPU will have to be altered so that the expanded virtual memory can be processed. Moreover, there is another disadvantage that the OS itself has to be modified to a major extent because the address section of the command and the address storing area are expanded to the same number of bits.
An object of the present invention is, therefore, to obviate the aforementioned disadvantages and provide a multiprocessor system whose virtual memory capacity can be expanded without entailing major modification of the OS.